fs_mgr: allow for zramsize to be specified as percentage of total memory

If the zramsize entry has a % size at the end, as in the following example:

	/dev/block/zram0 none swap defaults zramsize=25%

then we will set the value as that percentage of total RAM, as read by scanning
/proc/meminfo.

b/20760266 Seed common build allocated too much for zRAM-backed swap

Change-Id: I17c91d311ba99ae7adae112bfe1b38542ea69b80
Signed-off-by: Iliyan Malchev <malchev@google.com>

1 files changed, 21 insertions, 1 deletions

diff --git a/fs_mgr/fs_mgr_fstab.c b/fs_mgr/fs_mgr_fstab.c
index ab8f128..c200b05 100644
--- a/fs_mgr/fs_mgr_fstab.c
+++ b/fs_mgr/fs_mgr_fstab.c
@@ -15,10 +15,12 @@
  */
 
 #include <ctype.h>
+#include <errno.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <sys/mount.h>
+#include <unistd.h>
 
 #include "fs_mgr_priv.h"
 
@@ -72,6 +74,19 @@ static struct flag_list fs_mgr_flags[] = {
     { 0,             0 },
 };
 
+static uint64_t calculate_zram_size(unsigned int percentage)
+{
+    uint64_t total;
+
+    total  = sysconf(_SC_PHYS_PAGES);
+    total *= percentage;
+    total /= 100;
+
+    total *= sysconf(_SC_PAGESIZE);
+
+    return total;
+}
+
 static int parse_flags(char *flags, struct flag_list *fl,
                        struct fs_mgr_flag_values *flag_vals,
                        char *fs_options, int fs_options_len)
@@ -145,7 +160,12 @@ static int parse_flags(char *flags, struct flag_list *fl,
                 } else if ((fl[i].flag == MF_SWAPPRIO) && flag_vals) {
                     flag_vals->swap_prio = strtoll(strchr(p, '=') + 1, NULL, 0);
                 } else if ((fl[i].flag == MF_ZRAMSIZE) && flag_vals) {
-                    flag_vals->zram_size = strtoll(strchr(p, '=') + 1, NULL, 0);
+                    int is_percent = !!strrchr(p, '%');
+                    unsigned int val = strtoll(strchr(p, '=') + 1, NULL, 0);
+                    if (is_percent)
+                        flag_vals->zram_size = calculate_zram_size(val);
+                    else
+                        flag_vals->zram_size = val;
                 }
                 break;
             }